I've wanted to switch to nftables on some of my systems but found that some software or other depended on iptables (e.g. Docker Engine, Proxmox). Use nftables if you can get away with it but iptables-specific knowledge is still extremely relevant.

For the most part iptables is no more, iptables tools are now just wrappers to nftables. Technically you can still write iptables rules, and they will show up in nftables. Wouldnt recommend long term but its a good way to see the translation

That's not realalistic for most of the Linux world.

Soooo many systems are still using iptables even though we "should" be using nft everywhere.

If you're going to be a Linux Sys/Net Admin today, you need an understanding of both systems.